1. Field of the Invention:
The present invention relates to a distilling apparatus which is adapted to obtain extremely pure or ultrapure distilled water containing a very small amount of impurities from raw water.
2. Description of the Prior Art:
Distilled water of a high purity (also called "ultrapure water") which contains a very small amount of impurities is conventionally demanded by the electronics industry for manufacturing semiconductors and the pharmaceutical industry for manufacturing pharamceutical substances.
In particular, when manufacturing precise semiconductor devices such as integrated circuits (ICs) and large scale integrated circuits (LSIs), a large amount of distilled water is used in washing process and, therefore, the purity of the distilled water which is used can directly effect the production yield. For this reason, the stable production of extremely pure distilled water is an important point.
In a conventional distilling apparatus, heated raw water is supplied to a hydrophobic porous film and is brought into contact therewith, and vapor generated from the raw water filters through the hydrophobic porous film. However, since the raw water is directly supplied to one surface of the hydrophobic porous film, the proportion of vapor generated on the side of that surface is small, thus making it difficult for a large amount of vapor to filter through the film.
In addition, the hydrophobic porous film has a large number of small holes formed therein, and vapor which is generated from the surface of the raw water, which is in a state wherein it slightly penetrates the holes, filters therethrough. Thereafter, the filtered vapor is condensed by means of cooling water so as to obtain distilled water. However, when the vapor filters through the hydrophobic porous film, gases (e.g., carbonic dioxide gas and oxygen gas) as well as volatile substances which are dissolved in the raw water also evaporate and pass through the film. Therefore, the gases and volatile substances are dissolved in the condensed product, thus impeding the effort of increasing the degree of purity. In conventional apparatuses, no particular attention has been paid to this problem. One example of the prior art relating to this type of apparatus is that disclosed in U.S. Pat. No. 3,563,860.